Method of and apparatus for forming trenches



Jan. 8, 1929.

R. F. BENNETT METHOD 01"'A AND APPARATUS FOR FQRMING-,TENCHES Filed Jan. 7. 1927 2 sheets-sheet 1` ihm Jan. 8, l1.929. 1,698,529

R. F. BENNETT METHOD OF AND APPARATUS FOR FORMING TRENCHES Filed Jan. '2, 1927 2 sheets-sheet 2 3*,-15 bitter Patented dan. 8, i929,

itil?? 'RAYMOND F. BENNETT,

' ressa or PORTLAND, MAINE.

METHOD OF AND APPARATUS FOR ORMING TRENCHES.

Application filed January 7, 1927. Serial No. 159,675.

In forming trenchesv in shifting media, such als sand and particularly in sand where the tide ebbs and iiows, serious difficulties are encountered due to such natural conditions. On a characteristic contract which I have recently completed, these natural factors were particularly unfavorable. The contracty called for the laying of a pipe line several hundred feet long across a tidal fla-t where the average rise and fall of the tide was aboutnine feet. In addition, the topography was such that even at low water one end of the pipe line was always submerged and the gradient of the line varied considerably atdiflerent sections vthereof. This not only meant that work could only be done during lthe average few hours of low water, but that during the flood tide the sand would be washed back in the trench and had to be cleared out again when the tide ebbed. I saw at once that exist-ing methods would not suffice. ticable simply to excavate a wide trench and use flexible pipe joint, first on account of the filling in of the trench at each tidal change, and second, on account of the expense of ther flexible pipe joints. usual practice involving the driving of two paced lines or courses of tight sheeting, excavating the earth and sand therebetween, and bracing` the sheeting and completing the driving as the excavations proceeded 'because such a method would have required a large crew of men and inasmuch as work could only be done at low tide, the crew would have been idle too long in proportionprocedure and lower production cost are' factors. My invention is especially applicable however inthe excavating of compratively shallow trenchesin runny soils such as sand, lcpiioksand, or similar shifting meda and where the excavation has to be made For example, it was not pra-c- Nor could I follow theL in or'under water, as in flats and ,marshes subject to tidal overflow;

Broadly, my method involves the use of.v

a rmovable shield whichprovides an excavating chamber within which Vfull depth exea vation may be done as well as a vwork chamber within which the pipe or otherv work may be laid as the excavatingproceeds, the walls of the shield serving as stays forthe trench wallswhile theexcavation is being made, and the pipe laid or other work done and the shield itself being-`A intermittently moved 'ahead when the excavation within its confines is completed and used. In the particular piece of work in question, the exca-l vating machine wasmounted on a gantry which itself was located in :comparatively deep water even at low tldeso thatthe starting end of the pipe line was submerged.

The initial excavatingtherefore was begun inside of the shield so as to allowl the shield to settle -vertically into position by reason of its own weight plus such additional force o: weights as were necessary'to insure that it be sunk to the required depth. TVheni the excavating Ahad been `completed to full'depth within the snield and also to a slight depth in advance of the shield, and before the earth had time to fill in, the shield was pulled ahead by means of av tackle and harness connected with the fixed post or .dead manat thevfarA end of the pipe line course, for val distance as far as it was possible to hold the side banks fromcaving in. The excavating machine was then drawn forwardly by means of the same harness and tackle to a position where further excavation Vaheadof and within the shield could be accomplished, and

the operation was repeated until the entire trench had been excavated.

In the accompanying drawings iI Vhave shown my method and apparatus in connec,

tion with the particular piece ofwork for which it was originally designed, although it is to be understood that this treatment is illustrative and not'limiting.v

In the drawings: Fig. l is aside elevation partlyin section illustrating the'fpractice ofl "myy invention undertypical conditions.

. Fig. 2 is a fragmentaryplan view 'of Fig. l with the excavating machine l' illustrate details of 'constraction.1` j, n

` Fig. Slis a side elevation of myfshield'.

emoved to Fig. 4; is a vertical section along` the centre line of the shield.

Fig. 5 is a plan of F ig. 4, partly in horizontal section.

F 6 and 7 are typical cross sections on the lines 6 6 and 7-7 respectively of Fig. 3, and v Fig. 8 a modification for soft mud operation.

In Fig. 1 the starting end of the pipe line is represented as being submerged even at irons 3. These angle irons form cutting edges f which facilitate sinking the shield when beginning` operations and also assist in keeping the shield down to its proper depth when its lower edge ator slightly below the bottom` of the trench at all points and especially where changes in the gradient are made.

At the forward end of the side members A and B and projecting beyond the planking 1 is a series of cutter plates 4t disposed en echelon, as appears in Figs. 3 and 4'. These plates facilitate thepenetration ofthe shield through the soil vwhen the shield is rforced forwardly beyond the excavation D which it occupies. Preferably, the forward end of the shield is stepped: off, asv shown,`so that the forward cutting edges of the plates 4c are vertical or substantially vvertical'. Vertical disposition of these plates insuresV that the forward movement of the shield will be stopped by any hard. obstruction encoun tered, rather than permittingthe shield to ride up on the obstruction as would be the case of the forward cutting edges were inclined instead of vertical.

.The side members A and B constituting the sheeting are held in correct relation to each other by the bents C of which there may be any desired l number spaced along the shield towards its rcarlend, and by the cross struts 5 and k6,which struts define the excavation chamber D of the shieldn Each bent C is composed of side posts 7 joined together at their upper ends by girders 8 and diagonal-ly braced by braces 9 and cross struts 10, thespace beneath the struty 10 being left clear for pipe layingor other work which is to be done behind the strut 5 or in rear of the eX- cavation chamber D.

vThe strut 5 is disposed between a pair of vertical posts 11 at either side. of the shield and the shield is reinforced laterally by re-l rplanks 1 and to the forward strut 6. Be-

tween the posts 11 and the forward ends of the side members are diagonally disposed members 13 to which the side planks 1, the timbers 2 and the reinforcing members 12 are attached, and these members 13 project beyond the side planking and are fastened at their upper ends to the strut 6.

The side members A and are spaced apart sufficient-ly to afford suflicient space F Ybetweenthem for conveniently carrying on in the trench whatever work is to be done. rl`he outside contact surfaces of the side members A and B, above the angle-irons 3, may be spaced slightly farther apart at the forward ends ofthe shield than at the rear end so that the shield may be more easily pulled along in the trench, the pressure of the earth being thus somewhat relieved as the shield progresses because the contact surfaces tendto pull slightly away from the side earth as the shield progresses.

inasmuch the angle irons 3, are partly or wholly submerged in the'earth on the inner side, it vis desirable that these angle lirons should be strictly parallel to each other. This may be effected byV havingthe outer surfaces of each angle iron 3' and timber 2 flush at the forward end of the shield, and offset at the rear end half the amount on each side that the woodwork istapered. ln.

other words, the woodwork above the angleirons 3 is tapered, the angledrons themselves being parallel to each other.

Most of the excavating is done in the forward compartment or excavating chamber D of the shield between struts 5 and 6. excavating is also done just ahead ofthe shield as indicated at E. The sides of this chamber D are shown extending somewhat above the side reinforcing pieces 12. rlhese reinforcements protect the planking against the ,wear and hits of the excavating bucket, and also serve to guide the same. lf desired, these side pieces may be still further extended in height, so as to reach the surface of the water at a higher level, and thereby form guides for the bucket, so that excavating could he do-ne in greater depths of water than would otherwise be the case.

rlhe fc-.oustruetion work is done in the space between the side membersA A and l, and back of the strut This space may be `termed the construction chamber 7F.'

Procedure varies according to. "existing conditions. For example, if the vtrench is to -be begun abruptly, as on level ground, the

shield is` placed in position and the excavating beGun inside, so as to allow the shield to settle vertically into position by reason kof its own weight or addedforces or weights. Or if the slope assumed by the material will permit, a wide ditch with sloping sides may Some' grab bucket, operated by suitable power, or

y by any other method, means, or apparatus,

or by hand. rlhe excavated material may be deposited at one side to be later back-filled, or taken away entirely, or deposited bank ot' the shield as a backiill in one operation.

Assuming the shieid to be placed at the depth required the routine of Work, as in pipe laying, would be as follows: The excavating et the earth would be done to a slight depth just ahead ot the shield, as indicated at E, and to the full depth or below in the excavation chamber D, then beforethe earth has time to run in, the shield would be moved ahead as far as possible 'to hold the side banks from further caving. ln this manner progress along the trench would be made by alternately digging and pulling the shield ahead, but the digging and moving` ahead ot the shield may be done simultaneously in the most unstable soils, and possibly, to vgreater economic advantage in all soils. The movement of the shield may be accomplished by pulling` it ahead, as by the tackles 14, or by forcing it ahead from behind by` jacks, or by any other suitable means.

Before the shield is moved ahead, however, the trench already excavated in the shield, would he utilized for the laying ot pipe 15, or other work trom the rear ond up to a point just back of the strut 5. The shield is then moved ahead gradually until a suliicient length ot trench is open to allow the construction work in the same to proceed. Or the excavating ahead, the movement of 4the shield, and the pipe laying all might be carried on simultaneously.

In practice it has been found advisable to put sand bag weights in the upper part ot the bents C and resting` on the strut l0, to keep the rear end of the shield down, and to hold it from floating.

It water is present and the construction work must be carried on in the dry, damcontinuous method, thevcycle ot operations would be as follows: Excavated ahead, move shield ahead, pump out trench, lay pipe, and back-till in rear of shield or within rear end of the shield.

Various other modilications in method may b e practiced, as `for example, in the case of soft mud, as shown in Fig, 8. 'In such a case the beach instead ot being sand S, as indicated in Fig. l, may be mud M, as indicated in Fig. 8. In operations where. a pipe has to be "laid or like trenching done in an ooze or fluid mud, I vary my shield structure by a timber dam as indicated by the timbers 51 thus making of the opening at the end ofthe shield as indicated at D Ain 3 and 5, a more complete pocket from which the mud can be dredged. In this case the shields lare warped ahead into the sott mud without any advance excavation as indi-- cated at E in Fig. 3. On account ot the softness of such mud, the shields Al2 can be readily advanced and the How ot the mud held by the cross timbers 51. y

This variant in operation' is not essentially different from that heretofore de-- scribed in connection with work on a sand beach or beach of other dry or only partly wet nature. in any case the bucket is operated required in the open end between the members l2, there being sutlicient distance between the timber` 6 and thev timber or timbers 5 to give 'tree bucket or dredgeroom.

Wlhat I therefore'claim and desire to secure by Letters Patent is:

l. The method of forming trenches which consists in sinking a shield, in excavating within said shield, in excavating at the end ot said shield, and in advancing said shield into said excavation ahead-upon completion of the excavation within the shield to perd mit work to be completed in said excavation within t-he shield. i

2. The method of -forming trenches in shitting media., which consists in sinking a shield int-o the media, in excavating to full depth within said shield, in excavating slightly at the end of said shield, and in ad vancing said shield into said excavation ahead upon completion of the excavation within the shield to permit and tinally work to be completed in said excavation within the shield. 1

3. The method of forming trenches, which consists in sinking a shield having an excavating portion and a Work portionl in rear of said excavating portion, in excavating within said excavating portion, in excavating at the end ot said shield, and in advancing said shield into said excavation ahead upon completion of thev excavation within.

said shield to permit work to be completed in the excavation comprised within said Work portion.

t. The method of forming trenches in shifting media, which consists in sinking into said media a shield having an excavating portion and a work porton in rear of said excavating portion, in excavating t-o full depth within said excavating portion, in excavating slightly ahead of said shield, and in advancing said shield into said excavation ahead upon completion of the excavation within said shield t-o permit work to be completed in the excavation comprised within said work portion.

5. In apparatus for use with a trench excavator, a shield comprising spaced side members cross-connected to each other and sustained as an excavating` portion and a work portion in rear of said excavating portion.

6. In apparatus for use with a trench eX- cavator, a shield comprising spaced side members cross-connected to each other and sustained as an excavating portion and a work portion in rear of said excavating portion and having at their forwardends cutter members for facilitating the advance of the shield through the soil.

7. In apparatus for use with a trench excavator, a shield comprising spaced side members including bottom angle-irons and sheeting thereabove, said side members being cross-connected and sustained as an excavating portion and a work portion in rear of said excavating portion. i

8. In apparatus for use with a trench exn cavator, a shield comprising spaced side members including bottom angle-irons and sheeting thereabove, said side members being cross-connected and sustained as an excavating portion and a work portion in rear of said excavating portion, and having at their forward ends cutter members for facilitating the advance of the shield through the soil.

9. In apparatus for use with a trench excavator, a shield comprising spaced side members, a bent, a pair of spaced cross struts in advance of said bent, the space between said struts constituting an excavating portion and the space between said bent and the rearward strut constituting a work portion disposedin rear of said excavating portion.

l0. In apparatus for use with a trench excavator, a shield comprising spaced side members, a bent, a pair of spaced cross struts in advance of said bent, the space between said struts constituting an excavating portion and the space between said bent and the. rearward strut constituting a work portion disposed in rear of said excavating portion, the forward end of the shield being longitudinally reinforced and having a cutter for facilitating the advance of the shield through the soil.

l1. In apparatus for use with a trench excavator in shifting` media, a shield comprising spaced side members including bottoni angle irons, timbers carrying the same, and sheeting superposed on said timbers, a bent, a pair of spaced cross struts in advance of said bent the space between said struts constituting an excavating port-ion and the space between said bent and the rearn ward strut constituting a work portion disposed in rear of said excavating portion.

l2. In apparatus for use with a trench excavator in shifting media, a shield come prising spaced side members includingbottom angle irons, timbers carrying the same, and sheeting superposed on said timbers, a bent, a pair of spaced cross struts in advance of said bent, the space between said struts constituting yan excavating portion and the space between said bent and the rearward strut constituting a work portion disposed in rear of said excavating portion, the forward end of the lshield being longitudinally reinforced and having a cutter for faciiitating the advance of the shield througl'i the soil.

In testimonv whereof I ai'ix mv signature.

nAYMoND r. BENNETT. 

